Electric holding magnet serving as tripping device for ground leakage circuit breakers

ABSTRACT

The two legs of a holding magnet for ground leakage circuit breakers are arranged in juxtaposition and form a magnetic shunt. A permanent magnet at one end of the legs and the legs at such end are disposed between two pole pieces. Each of the pole pieces contacts a corresponding one of the legs and a corresponding pole face of the permanent magnet. Both pole pieces comprise a magnetic material having a higher magnetic saturation than the material of the legs.

United States Patent 1 Flohr Oct. 2, 1973 v 1 ELECTRIC HOLDING MAGNETSERVING AS TRIPPING DEVICE FOR GROUND LEAKAGE CIRCUIT BREAKERS Inventor:Peter Flohr, Regensburg, Germany Siemens Aktiengesellschaft, Berlin andMunich, Germany Filed: Nov. 15, 1971 Appl. No.: 198,796

Assignee:

Foreign Application Priority Data Nov. 18, 1970 Germany P 20 56 627.2

References Cited UNITED STATES PATENTS 1/1967 Zocholl 335/230 FOREIGNPATENTS OR APPLICATIONS 251,682 1/1967 Austria 335/236 PrimaryExaminerl-larold Broome Att0meyArthur E. Wilfond et a1.

[57] ABSTRACT The two legs of a holding magnet for ground leakagecircuit breakers are arranged in juxtaposition and form a magneticshunt. A permanent magnet at one end of the legs and the legs at suchend are disposed between two pole pieces. Each of the pole piecescontacts a corresponding one of the legs and a corresponding pole faceof the permanent magnet. Both pole pieces comprise a magnetic materialhaving a higher magnetic saturation than the material of the legs.

5 Claims, 4 Drawing Figures Patented Oct. 2, 1973 3,763,450

non I 5 5 1 L5 2 1 2" 1 2 2a 1a [I113 10 10 #12 a n '7 11 '8 17 5 5 S 5L J LBJ; Fig.2 Fig.3 Fig.4

PA /0i? ART ELECTRIC HOLDING MAGNET SERVING. AS TRIPPING DEVICE FORGROUND LEAKAGE CIRCUIT BREAKERS The invention relates to an electricholding magnet. More particularly, the invention relates to an electricholding magnet serving as a tripping device for ground leakage circuitbreakers.

The electric holding magnet of the invention serving as a trippingdevice for ground leakage circuit breakers, has two legs comprisingmaterial of high magnetic conductivity in juxtaposition. An excitationwinding is mounted on one end of at least one of the legs. A permanentmagnet is positioned at the other end of the legs. A magnetic shunt isformed of portions of the legs in close mutual proximity and extendsbetween the permanent magnet and the excitation winding.

A holding magnet of the aforedescribed type is disclosed in GermanPublished Patent Application No. 1,665,851. The permanent magnet ispositioned in opposing recesses of the legs. The legs comprise materialof high magnetic conductivity. The holding magnet has the advantage thatthe magnetic shunt provides it with increased trigger sensitivity.Furthermore, its geometric dimensions are reduced, because the magneticshunt formed by the closely adjacent portions of the legs has only asingle air gap.

An object of the invention is to provide an electric holding magnethaving reduced geometric dimensions, particularly in width, withoutincreasing the excitation power and reducing the trigger sensitivity.

Another object of the invention is to provide an electric holding magnetof simple compact structure which functions with efficiency,effectiveness and reliability.

To solve the aforedescribed problem, the electric holding magnet of theinvention which serves as a tripping device has its legs at the end withthe permanent magnet, positioned with the permanent magnet between twoplates. The plates comprise material of a higher magnetic saturationthan the material of the legs. Each of the plates is in contact with anarea of a corresponding one of the legs anda correponding face of thepermanent magnet.

An electric holding magnet serving as a tripping device for groundleakage circuit breakers has two juxtaposed legs comprising material ofhigh magnetic conductivity, an excitation winding mounted on one end ofat least one of the legs, and a permanent magnet atthe other ends of thelegs. Portions of the legs in close mutual proximity form a magneticshunt extending between the permanent magnet and the excitation winding.In accordance with the invention, the holding magnet comprises a pair ofspaced substantially parallel plates comprising material of highermagnetic saturation than the material of the legs. The permanent magnetand the legs at their other ends are positioned between the plates. Eachof the plates contacts an area of a corresponding one of the legs and acorresponding pole face of the permanent magnet.

The plates completely cover the corresponding pole faces of thepermanent magnet.

The plates contact over large surface areas the portions of thecorresponding legs forming the magnetic shunt.

A layer of non-magnetic material between the portions of the legs formsthe magnetic shunt.

The legs comprise a nickel-iron alloy having to by weight of nickel andthe plates comprise soft iron.

In order that the invention may be readily carried into effect, it willnow be described with reference to the accompanying drawing, wherein:

FIG. I is a schematic circuit diagram of a ground leakage circuitbreaker;

FIG. 2 is a side elevation of a known electric holding magnet which maybe utilized in the ground leakage circuit breaker of FIG. I;

FIG. 3 is a side elevation of an embodiment of an electric holdingmagnet of the invention; and

FIG. 4 is a front view of the embodiment of FIG. 3 of an electricholding magnet of the invention.

In the FIGS., the same components are identified by the same referencenumerals.

In FIG. 1, the ground leakage circuit breaker has a summing currenttransformer having a closed annular magnetic core 22. The transformerhas two primary windings comprising two lines 23 and 24 extendingthrough the magnetic core 22, and a secondary winding 25 wound on saidmagnetic core. The secondary winding 25 is connected to the excitationwinding of a holding magnet 27 which serves as the tripping device for aswitch actuator 26. The actuator 26 is mechanically coupled, via aswitching rod 28, to two switch contacts 29 interposed in the two lines23 and 24.

A load 31 in a grounded metal housing 30 is connected to one phase andthe ground conductor of the power supply system via the lines 23 and 24.Normally, just as much current flows through the line 24 from the load31 back to the line as flows through the line 23 to said load.Therefore, no voltage is induced in the secondary winding 25 of thesumming current transformer. If, however, there is a path to the housing30 from the load 311, part of the current supplied to said load from thesystem via the line 23, namely, the leakage current, returns to thesystem via the grounded housing 30. That is, the current returning fromthe load 31 to the system via the line 24 is smaller than the currentflowing to the load via the line 23. The equilibrium of the currentsflowing through the summing current transformer is therefore disturbed,and a voltage is induced in the secondary winding 25. The holdingmagnet-therefore acuates, opens or unlatches the switch actuator 26, andthe switch contacts 29 are opened.

The known holding magnet shown in FIG. 2 has two flat .legs I and 2facing each other at their surfaces and is under the influence of atension spring 4. The leg I carries at the end near an armature 3 awinding 5 serving as the excitation winding. Each of the legs 1 and 2has at the other end a recess 17 and 18, respectively, which face eachother and in which a permanent magnet 6 is positioned in a mannerwhereby each leg contacts a corresponding pole face of said permanentmagnet.

The legs I and 2 have extending portions 7 and 8, respectively, facingeach other. The extending portions 7 and 8 of the legs 11 and 2 form amagnetic shunt which extends between the excitation winding 5 and theother ends of the legs, at which the permanent magnet 6 is positioned. Anarrow air gap 9 is provided between the extending portions 7 and 8 ofthe legs I and 2. A thin, non-magnetic layer, for example, an aluminumfoil, may be positioned in the air gap 9. The legs 1 and 2 are heldtogether by a bolt 10 extending through apertures formed through theirextending portions 7 and 8.

When the excitation winding is energized, it produces a magnetic fluxwhich acts upon the magnetic flux produced in the legs 1 and 2 by thepermanent magnet 6. If the part of the magnetic flux which emanates fromthe permanent magnet 6 and flows through the armature 3 and the legs 1and 2 at the ends near said armature is sufficiently compensated by themagnetic flux emanating from the excitation winding 5, said armature islifted from said legs by force of the tension spring 4, whereby theswitch actuator 26 (FIG. 1) of the ground leakage circuit breaker isactuated, opened and unlatched.

The compensating flux emanating from the excitation winding 5, which issufficient to permit the lifting of the armature 3 by the spring 4, neednot be very great, since the greater part of the magnetic flux emanatingfrom the permanent magnet 6 goes through the magnetic shunt formed bythe extending portions 7 and 8 of the legs 1 and 2 and is magneticallyhighly conductive. The aforedescribed compensating flux can go throughthe magnetic shunt and practically does not have to take the paththrough the permanent magnet 6, which is a poor magnetic conductor.

FIGS. 3 and 4 show the holding magnets of the invention. In the holdingmagnets of FIGS. 3 and 4 the flat legs 1 and 2 face each other at theirsurfaces. The ends of the legs 1 and 2 at which the permanent magnet 6is positioned and said permanent magnet are positioned between twospaced plates or pole pieces. The plates 11 and 12 comprise material ofhigher magnetic saturation, that is, higher saturation induction, thanthe material of legs 1 and 2.

An aluminum foil, having a thickness of 10 microns, for example, may bepositioned between portions la and 2a of the legs 1 and 2, respectively.The portions la and 2a of the legs 1 and 2 are in juxtaposition and formthe magnetic shunt. This has the effect that, on the one hand, themagnetic resistance of the magnetic shunt is still large enough that amagnetic flux sufficient to produce an adequate holding force goesthrough the armature 3 and, on the other hand, that the magneticresistance of said magnetic shunt is still small enough that the holdingmagnet has a sufficiently high trigger sensitivity.

The surface of the plate 11 is in direct contact with the leg 1 and theSouth pole face S of the permanent magnet 6. The surface of the plate 12is in direct contact with the leg 2 and the North pole face N of thepermanent magnet 6. The legs 1 and 2 and the armature 3 comprise, forexample, a nickel-iron alloy having 70 to 80 percent by weight of nickel(mu metal). The plates 11 and 12 advantageously comprise soft steel,which has twice the magnetic saturation, that is, twice the saturationinduction, of the nickel-iron alloy. Soft steel is obtained from highcarbon raw steel by decarbonizing the raw steel by heating it to atemperature above the melting point, that is, in the molten condition.

The magnetic tripping circuit comprising the legs 1 and 2 and thearmature 3 of the holding magnet of the invention is of high magneticconductivity and is not influenced by the plates 11 and 12. The plates11 and 12 therefore have no effect on the trigger sensitivity of theholding magnet and they need not consist of high permeability material.

The magnetic flux required to obtain the holding force for the armature3 is transferred from the permanent magnet 6 to the legs 1 and 2 via theplates 11 and 12. It is therefore advantageous if the plates 11 and 12completely cover the pole faces of the permanent magnet 6. It is alsopreferable that the plates 1 l and 12 contact the portions la and 2a ofthe legs 1 and 2 forming the magnetic shunt in a large surface area.

The magnetic flux transferred from the permanent magnet 6 to the legs 1and 2 via the plates 11 and 12, of a material having higher magneticsaturation, or saturation induction, than the material of said legs, isgreater than the magnetic flux transferred by plates 11 and 12 of thesame geometric dimensions but comprising a material having the samemagnetic saturation, or saturation induction, as said legs.

As seen from FIGS. 1 and 3, for the foregoing reasons, the holdingmagnet of the invention has considerably less width B than the knowntripping magnet. If the plates 11 and 12 utilized comprise soft steel,the reduction of the width can be approximately 35 percent, whereby upto 50 percent by weight of the relatively expensive nickel-iron alloy,of which the legs 1 and 2 consist, can be saved.

While the invention has been described by means of a specific exampleand in a specific embodiment, it should not be limited thereto, forobvious modifications will occur to those skilled in the art withoutdeparting from the spirit and scope of the invention.

1 claim:

1. An electric holding magnet serving as a tripping device for groundleakage circuit breakers and having two juxtaposed legs comprisingmaterial of low magnetic resistance, and excitation winding mounted onat least one of the legs, an armature also of a material of low magneticresistance engageable with one end of the legs, a permanent magnetengaging the other end of the legs and formed with opposite pole faces,portions of the legs being in close proximity and forming a magneticshunt extending between the permanent magnet and the armature, and apair of mutually spaced plates formed of material having a highermagnetic saturation than that of the legs, said permanent magnet andpart of the legs being disposed between said plates so that each of saidplates abuts an area of one of the legs, respectively, and one of thepole faces, respectively, of said permanent magnet.

2. An electric holding magnet as claimed in claim 1, wherein the platescompletely cover the corresponding pole faces of the permanent magnet.

3. An electric holding magnet as claimed in claim 1, wherein the platescontact over large surface areas the portions of the corresponding legsforming the magnetic shunt.

4. An electric holding magnet as claimed in claim 1, further comprisinga layer of non-magnetic material between the portions of the legsforming the magnetic shunt.

5. An electric holding magnet as claimed in claim 1, wherein the legscomprise a nickel-iron alloy having to percent by weight of nickel andthe plates comprise soft iron.

1. An electric holding magnet serving as a tripping device for groundleakage circuit breakers and having two juxtaposed legs comprisingmaterial of low magnetic resistance, and excitation winding mounted onat least one of the legs, an armature also of a material of low magneticresistance engageable with one end of the legs, a permanent magnetengaging the other end of the legs and formed with opposite pole faces,portions of the legs being in close proximity and forming a magneticshunt extending between the permanent magnet and the armature, and apair of mutually spaced plates formed of material having a highermagnetic saturation than that of the legs, said permanent magnet andpart of the legs being disposed between said plates so that each of saidplates abuts an area of one of the legs, respectively, and one of thepole faces, respectively, of said permanent magnet.
 2. An electricholding magnet as claimed in claim 1, wherein the plates completelycover the corresponding pole faces of the permanent magnet.
 3. Anelectric holding magnet as claimed in claim 1, wherein the platescontact over large surface areas the portions of the corresponding legsforming the magnetic shunt.
 4. An electric holding magnet as claimed inclaim 1, further comprising a layer of non-magnetic material between theportions of the legs forming the magnetic shunt.
 5. An electric holdingmagnet as claimed in claim 1, wherein the legs comprise a nickel-ironalloy having 70 to 80 percent by weight of nickel and the platescomprise soft iron.